Primer on Designing Facilities

When considering, planning, or constructing a bike facility, the first step
is to identify the project scope. As more detailed information becomes
available on site limitations, construction cost, and funding project impacts,
the scope will be refined through the design development process. Basic
considerations in defining the scope are facility type (on street, off street,
equipment), paving, drainage, structures, and design guidelines used to identify
dimensions such as width of paths. The following text provides some basics
in identifying the project scope.

When developing the cost of on-street bicycle facilities and shared use paths,
the user will need to know how to select construction materials, recommend
dimensions, and decide on a path surface. The following is a primer for
design consideration of bicycle facilities. Pavement design focuses
primarily on shared use paths and other off street facilities. Bicycle
facilities on roadways are considered to be a minor part of the structural
design of the roadway and are therefore not included as part of the primer. This
primer should be used in conjunction with the 1999 AASHTO Guide for the Development
of Bicycle Facilities.

On Street Facility

On street facilities consist primarily of paved shoulders, wide curb lanes,
and bike lanes. All are part of the roadway surface that is also used
by motor vehicles. Structural requirements of the road bed including
pavement depth are dictated by motor vehicles.

Paved shoulders

Critical dimensions:

Less than 4 feet (1.2m): any additional width of paved shoulder is preferred
than no facility at all, but below 4 feet a shoulder should not be designated
or marked as a bicycle facility.

4 feet (1.2m): minimum width to accommodate bicycle travel measurement
must be of useable width and should NOT include the gutter pan or any area
treated with rumble strips

5 feet (1.5m) or more: minimum width recommended from the face of a guardrail,
curb or other barrier

Wide Outside Lanes

Critical dimensions:

14 feet (4.2m): recommended width for wide outside lane width must be useable
and measurement should be from the edge line or joint of the gutter pan to
the lane line

15 feet (4.5m): preferred where extra space required for maneuvering (e.g.
on steep grades) or to keep clear of on-street parking or other obstacles.

Continuous stretches of lane 15 feet (4.5m) or wider may encourage the undesirable
operation of two motor vehicles in one lane. Where this much width is
available, it is recommended to more seriously consider striping bike
lanes or shoulders.

Bicycle Lanes

Critical dimensions:

Bicycle lane width:

4 feet (1.2m): minimum width of bike lane on roadways with no curb and
gutter,

5 feet (1.5m): minimum width of bike lane when adjacent to parking, from
the face of the curb or guardrail,

Off Street Facility (typically shared use paths)

Standards recommend the width be 10 feet or 3 meters for a two-way, shared
use path on a separate right of way. Other critical measurements include:

8 feet (2.4m) may be used where bicycle traffic is expected to be low at
all times, pedestrian use is only occasional, sightlines are good, passing
opportunities are provided, and maintenance vehicles will not destroy the
edge of the trail,

12 feet is recommended where substantial use by bicycles, joggers, skaters,
and pedestrians is expected, and where grades are steep (see later),

2 feet of graded area should be maintained adjacent to both sides of the
path,

3 feet of clear distance should be maintained between the edge of the trail
and trees, poles, walls, fences, guardrails or other lateral obstructions,

8 feet of vertical clearance to obstructions should be maintained; rising
to 10 feet in tunnels and where maintenance and emergency vehicles must operate.

Drainage

The AASHTO Guide recommends a cross slope of 2%. Other
considerations to ensure adequate drainage include:

slope the trail in one direction rather than having a crown in the middle
of the trail,

ensure a smooth surface to prevent ponding and ice formation,

place a ditch on the upside of a trail constructed on the side of a hill,

place drainage grates, utility covers etc out of the travel path of bicyclists,

seeding, mulching, and sodding of slopes, swales and other erodible areas
should be included in the cost.

Proper drainage is one of the most important factors affecting pavement performance.
Proper drainage entails efficient removal of excess water from the trail. Surface
water runoff should be handled using swales, ditches, and sheet flow. Catch
basins, drain inlets, culverts and underground piping may also be necessary.
These structures should be located off of the pavement structure.

Structures

An overpass, underpass, small bridge, drainage facility or
facility on a highway bridge may be necessary to provide continuity to a bicycle
path.

The critical dimensions to use in designing underpasses, overpasses, bridges
and tunnels, include:
(a) the minimum width of the trail (usually 10 feet) should be maintained
through the structure,
(b) the clear distance of two feet on either side of the trail surface
should also be maintained through the structure - otherwise, riders will tend
to ride in the center of the trail to stay away from the wall or railing of
the structure,
(c) an overhead clearance of 10 feet (8 feet with good horizontal and
vertical clearance, good sightlines etc) should be maintained through an underpass
or tunnel,
(d) railings, fences or barriers on both sides of a path on a structure
should be at least 42 inches (1.1m) high, and where they are higher than this
a rub rail should be provided at the approximate handlebar height of 42 inches,
(e) clearances should allow for maintenance and emergency vehicles, as
should the strength of the bridge (live loading).

Where it is necessary to retrofit a bicycle path onto an existing highway
bridge, several alternatives should be considered in light of what the geometrics
of the bridge will allow.

(a) Bicycle path across the bridge on one side. This should be done where
(1) the bridge facility will connect to a bicycle path at both ends; (2) sufficient
width exists on that side of the bridge or can be obtained by widening or restriping
lanes; and (3) provisions are made to physically separate bicycle traffic from
motor vehicle traffic as discussed above.
(b) Wide curb lanes or bicycle lanes over the bridge. This may be advisable
where (1) the bicycle path transitions into bicycle lanes at one end of the
bridge; and (2) sufficient width exists or can be obtained by widening or restriping.
(c) Use existing sidewalks as one-way or two-way facilities. This may
be advisable where (1) conflicts between bicyclists and pedestrians will not
exceed tolerable limits; and (2) the existing sidewalks are adequately wide.
Under certain conditions, the bicyclist may be required to dismount and cross
the structure as a pedestrian.

Because of the large number of variables involved in retrofitting bicycle
facilities onto existing bridges, compromises in desirable design criteria
are often inevitable. Therefore, the width to be provided is best determined
by the designer, on a case-by-case basis, after thoroughly considering all
the variables.

Lighting

Shared use paths in urban and suburban areas often
serve travel needs both day and night, for example commuter routes and trails
accessing college campuses. Fixed source lighting improves visibility along
trails and at intersections, and is critical for lighting tunnels and underpasses.
The AASHTO guide recommends using average maintained illumination levels of
between 5 and 22 lux, and the Florida DOT recommends 25 as the average initial
lux.

Signing and Marking

Adequate signing and marking are essential
on shared use paths, just as they are on streets and highways. Trail
users need to know about potential conflicts, regulatory information, destinations,
cross streets etc. The Manual on Uniform Traffic Control Devices (MUTCD)
provides some minimum traffic control measures that should be applied.

Striping: a yellow center line stripe is recommended where trails are busy,
where sight distances are restricted, and on unlighted trails where night time
riding is expected. The line should be dashed when adequate passing sight distance
exists, and solid when no passing is recommended.
A solid white line may be used to separate pedestrians from bicycle/blading
traffic, and solid white edge stripes may also be useful where nighttime riding
is expected.

Warning signs: a range of warning signs can be used to inform users that
recommended design criteria cannot be met, for example curve radii or grades.

Informational signs: trail users need to know where they are, where they
are going, what cross streets they are crossing, how far destinations are away,
and what services are available close to the trail. The MUTCD has information
on the appropriate signs to use in these instances. Although not in the MUTCD,
many trails post signs encouraging uniform trail user etiquette (e.g. give
audible signal when passing).

Intersection markings and signs: pavement marking and signs at intersections
should channel users to cross at clearly defined locations and indicate that
crossing traffic is to be expected. Similar devices to those used on roadways
(i.e. stop and yield signs, stop bars) should be used on trails as appropriate.

The AASHTO Guide notes that in addition to traditional warning signs in advance
of intersections, motorists can be alerted to the presence of a trail crossing
through flashing warning lights, zebra-style or colored pavement crosswalks,
raised crosswalks, signals, and neck-downs/curb-bulbs.

Path Surfaces

The type of surface that will be provided is an
important consideration in design. A hard surface, such as cement or asphalt,
will generally see cyclists operating at a faster speed than a soft surface,
is more expensive to install. A soft surface trail will discourage or prevent
in-line skating but may enable horse-back riders to share the trail and is
less expensive to install. Factors such as weather conditions and soil types
can affect the choice of asphalt, concrete, or crushed rock.

Each surface material type has advantages and disadvantages. Soft surface
materials are low cost, but require substantial maintenance and are not suitable
for many of the recreational activities today's trails and paths are used for.
Hard surface materials, specifically concrete and asphalt, provide years of
service with low maintenance.

The key to designing quality pavement surfaces, particularly asphalt surfaces,
depends on the following criteria.

Design to meet the needs of the anticipated users.

Follow guidelines in AASHTO Guide for the Development of Bicycle Facilities
for path width, sight distances, clearance, grade, signage, etc.

Under most circumstances, a 2-3 inch (50-75 mm) thick asphalt concrete top
course placed on a 6 inch (150 mm) thick aggregate subbase is suitable for
a bikeway pavement structure. While loads on bicycle paths will be substantially
less than highway loads, paths should be designed to sustain without damage
wheel loads of maintenance vehicles that are expected to use or cross the path. Path
width of 12 ft allows service vehicles to travel on the path without encroaching
and therefore potentially damaging the edge of pavement and the subbase.

In areas where climates are extreme, the effects of freeze-thaw cycles should
be anticipated in the design phase. At driveway crossings of bicycle paths,
the highway or driveway should be paved a minimum of 10 feet on each side of
the crossing to reduce the amount of gravel being scattered along the path
by motor vehicles.

Development of pavement section recommendations assumes a properly prepared
sub-grade. The subgrade should be cleared of vegetation and compacted. The
subgrade or compacted area should extend at least two feet beyond the edge
of pavement.

Bike paths and trails should be constructed to match the existing topography
as closely as possible, however, longitudinal slopes should not exceed five
percent and a cross slope of two percent is desirable to provide adequate drainage
away from the pavement surface. Maintenance
Properly constructed asphalt pavement using an appropriate mix design
requires minimal maintenance. Providing proper drainage is also a key to reducing
maintenance costs.

Maintenance is generally divided into two categories, preventative maintenance
and corrective maintenance. Preventive maintenance is performed on a regularly
scheduled basis to improve the life of the pavement and decrease the rate of
deterioration. Corrective maintenance is performed to correct a specific pavement
failure or distress area.

Normal periodic maintenance, depending on path location, drainage and climate,
should include sweeping the trail of debris.